This invention relates to a mobile communication system and to a method of dispersing data in this system. More particularly, the invention relates to a mobile communication system, which has a plurality of radio network controllers (RNC) and a number of radio base stations (Node B) connected to each of the radio network controllers, for sending and receiving user data between a host network (CN) and mobile stations (UE) via the radio network controllers and radio base stations, and to a method of dispersing data in this system.
The commercialization of CDMA (Code Division Multiple Access) communication systems is proceeding at a rapid pace. Commercial service for wideband CDMA (W-CDMA) systems, which are for exchanging not only voice and still pictures that form the principal service at the present time but also large quantities of data such as moving pictures, also has begun. The specifications for these have been set by the 3GPP (3rd Generation Partnership Project), which is an organization for standardizing 3rd generation mobile communication systems. The study of various specifications and their addition to existing specifications is continuing with the goal of attaining systems that can implement services having a quality higher presently available.
FIG. 18 is a diagram showing an overview of a W-CDMA system that is compliant with current 3GPP specifications. The system comprises nodes of four types, namely a host network (CN: Core Network) 100, radio control networks (RNC) 101_0 to 101—n, radio base stations (Node B) 102_0 to 102—n, and a mobile station (UE: User Equipment) 103. The nodes 100, 101_0 to 101—n and 102_0 to 102—n are physically connected (in a wired section) by ATM (Asynchronous Transfer Mode) transmission paths and IP (Internet Protocol) transmission paths, etc. The radio base stations 102_0 to 102—n are connected to the mobile station 103 by radio signals (in a wireless section). Iu represents an interface between the radio network controllers 101_0 to 101—n and the core network 100, Iur an interface between the radio network controllers 101_0 to 101—n, Iub an interface between the radio network controllers 101_0 to 101—n and radio base stations 102_0 to 102—n, and Uu an interface between the radio base stations 102_0 to 102—n and mobile station 103.
FIG. 19 is an explanatory view illustrating the flow of user data at the time of communication. User data is transmitted from the CN 100, which accommodates a switch, server and database, etc., to the RNC (SRNC: Serving RNC) 101_0 that controls UEs 103_0, 103_1, via the Iu line. In a case where a UE resides in a cell 104_1 under the control of SRNC 101_1 (i.e., in the case of UE 103_0), the user data is transmitted from SRNC 101_0 to Node B 102_1, which accommodates this cell, via the Iub line and thence is transmitted to UE 103_0 via the Uu interface (see the bold solid line in FIG. 19). On the other hand, if the UE resides in a cell 104_5 under the control of an RNC (DRNC: Drift RNC) 101_1 other than the SRNC 101_0 (i.e., in the case of UE 103_1) owing to movement of the UE, then the user data is transmitted from SRNC 101_0 to DRNC 101_1 via the Iur line, from DRNC 101_1 to Node B 102_5, which accommodates this cell, via the Iub line, and thence to the UE 103_1 via the Uu interface (see the bold dashed line in FIG. 19). It is assumed that the RNC that controls the UE 103_1 is SRNC even though this UE moves.
With high-speed data communication such as HSDPA (High Speed Data Packet Access) covered extensively as next-generation communication technology, the quantity of user data is increased greatly. As a result, the band required in the transmission paths of the interfaces Iu, Iur, Iub, etc., is widened greatly and it is necessary to improve the accommodating capability and processing capability at each node by a wide margin.
Further, in a mobile communication system, the conditions of use (traffic) fluctuate depending upon the time of day and location. If the traffic becomes unbalanced, a wider band and greater processing capability become necessary at locations where traffic concentrates in comparison with a situation in which there is no imbalance.
If such a marked increase in band and processing capability owing to higher speed of communication and marked increase in band and processing capability owing to traffic imbalance overlap, the load imposed upon the system will fluctuate violently. This can lead to system instability and degrade the efficiency of utilization of the entire system, thereby diminishing cost performance greatly. FIG. 20 is a diagram useful in describing the influence of traffic fluctuation upon the system. The band used on each transmission path is indicated by the thickness of the corresponding transmission path. In FIG. 20, traffic concentrates at SRNC 101_0, surplus band remaining at SRNC 101_0 diminishes and processing capability becomes inadequate. At DRNC 101_1, however, traffic is sparse, there is an abundance of surplus band and processing capability is adequate.
An approach that may be adopted in such case is to employ a design that furnishes the band and processing capability with latitude so as to be capable of dealing with large fluctuations in load. However, it is predicted that this will lead to an enormous increase in the size of circuitry, the size of the system and cost of development, etc. Cost performance declines greatly. For this reason, there is prior art so adapted as to disperse traffic when traffic becomes concentrated (Patent References 1 to 5). According to Patent Reference 1, which deals with a mobile communication system constituted by a plurality of radio base stations, a mobile telephone exchange calculates the call-channel rate of use of each mobile station from the number of call channels used by all radio base stations and the number of call channels used by each base station and, when the call-channel rate of use of a prescribed base station exceeds a threshold value, reduces traffic by lowering the radio transmission outputs of this radio base station. According to Patent Reference 2, when the call-channel rate of use of a base station that is the destination of movement at the time of handover is greater than a threshold value, handover to this radio base station is restricted. According to Patent Reference 3, a radio base station itself monitors the state of traffic concentration and, when concentration of traffic is detected, lowers the control-channel signal level, thereby reducing the size of the communication area and lowering traffic. According to Patent Reference 4, which deals with a digital mobile communication system in which communication between terminal stations that belong different repeater stations is performed via a single exchange, the traffic load is dispersed without control signals, which are sent and received between the repeater stations and exchange, becoming concentrated in a specific line. According to Patent Reference 5, areas (sub-areas) in which traffic density is low are consolidated into one radio area, and communication of incoming and outgoing calls of each area is performed by a single base station apparatus, thereby improving the efficiency of utilization of lines connected to a public digital network.
However, in none of these examples of the prior art is user data, which is sent and received between a core network and a prescribed radio base station, dispersed to a plurality of transmission paths between the core network and the prescribed radio base station upon taking transmission-path traffic into account. Further, none of these examples of the prior art reduce traffic on a transmission path or at a node where traffic has concentrated and continue communication upon allocating the amount of reduction to transmission paths or nodes where traffic has not concentrated. Further, none of these examples of the prior art contemplate dispersing traffic upon regarding amount of user data as traffic.    Patent Reference 1: Japanese Patent Application Laid-Open No. 5-63635    Patent Reference 2: Japanese Patent Application Laid-Open No. 6-164477    Patent Reference 3: Japanese Patent Application Laid-Open No. 9-163435    Patent Reference 4: Japanese Patent Application Laid-Open No. 8-205235    Patent Reference 5: Japanese Patent Application Laid-Open No. 8-307930